Pangenesis
Encyclopedia
Pangenesis was Charles Darwin
's hypothetical mechanism for heredity
. He presented this 'provisional hypothesis' in his 1868 work The Variation of Animals and Plants under Domestication
and felt that it brought 'together a multitude of facts which are at present left disconnected by any efficient cause'. The etymology of the word comes from the Greek
words pan (a prefix meaning "whole", "encompassing") and genesis ("birth") or genos ("origin").
Much of Darwin's pangenesis theory was speculatively based on inheritance of tiny heredity particles he called gemmules
that could be transmitted from parent to offspring. Darwin emphasized that only cells could regenerate new tissues or generate new organisms. He posited that atomic sized gemmules formed by cells would diffuse and aggregate in the reproductive organs.
phenomena, such as cellular regeneration
. His pangenesis theory was criticised for its Lamarckian premise that parents could pass on traits acquired
in their lifetime. Lamarckism fell from favour after August Weismann's
research in the 1880s indicated that changes from use (such as lifting weights to increase muscle mass) and disuse (such as being lazy and becoming scrawny) were not heritable. Some Lamarckian principles, however, have not been entirely discounted and some of Darwin's pangenesis principles (in this regard) do relate to heritable aspects of phenotypic plasticity
, while the status of gemmules has been firmly rejected. Darwin himself had noted that "the existence of free gemmules is a gratuitous assumption"; by some accounts in modern interpretation, gemmules may be considered a prescient mix of DNA, RNA, proteins, prions, and other mobile elements that are heritable in a non-Mendelian manner at the molecular level.
, he also stipulated that certain traits could be passed through organisms but would only develop depending on the sex of the organism in question.
conducted wide-ranging inquiries into heredity which led him to refute Charles Darwin's hypothetical theory of pangenesis. In consultation with Darwin, he set out to see if gemmules were transported in the blood. In a long series of experiments in 1869 to 1871, he transfused the blood between dissimilar breeds of rabbits, and examined the features of their offspring http://www.abc.net.au/rn/science/ss/stories/s216074.htm. He found no evidence of characters transmitted in the transfused blood . Darwin challenged the validity of Galton's experiment, giving his reasons in an article published in 'Nature'http://darwin-online.org.uk/content/frameset?itemID=F1751&viewtype=side&pageseq=1 where he wrote: "Now, in the chapter on Pangenesis in my Variation of Animals and Plants under Domestication, I have not said one word about the blood, or about any fluid proper to any circulating system. It is, indeed, obvious that the presence of gemmules in the blood can form no necessary part of my hypothesis; for I refer in illustration of it to the lowest animals, such as the Protozoa, which do not possess blood or any vessels; and I refer to plants in which the fluid, when present in the vessels, cannot be considered as true blood." He goes on to admit: "Nevertheless, when I first heard of Mr. Galton's experiments, I did not sufficiently reflect on the subject, and saw not the difficulty of believing in the presence of gemmules in the blood."
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
's hypothetical mechanism for heredity
Heredity
Heredity is the passing of traits to offspring . This is the process by which an offspring cell or organism acquires or becomes predisposed to the characteristics of its parent cell or organism. Through heredity, variations exhibited by individuals can accumulate and cause some species to evolve...
. He presented this 'provisional hypothesis' in his 1868 work The Variation of Animals and Plants under Domestication
The Variation of Animals and Plants under Domestication
The Variation of Animals and Plants under Domestication is a book written by Charles Darwin that was first published in January 1868.A large proportion of the book contains detailed information on the domestication of animals and plants but it also contains in Chapter XXVII a description of...
and felt that it brought 'together a multitude of facts which are at present left disconnected by any efficient cause'. The etymology of the word comes from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
words pan (a prefix meaning "whole", "encompassing") and genesis ("birth") or genos ("origin").
Much of Darwin's pangenesis theory was speculatively based on inheritance of tiny heredity particles he called gemmules
Gemmules
Gemmules were imagined particles of inheritance proposed byCharles Darwin as part of his Pangenesis theory. This appeared in his book The Variation of Animals and Plants under Domestication, published in 1868, nine years after the publication of his famous book On the Origin of Species.Gemmules,...
that could be transmitted from parent to offspring. Darwin emphasized that only cells could regenerate new tissues or generate new organisms. He posited that atomic sized gemmules formed by cells would diffuse and aggregate in the reproductive organs.
Overview
Darwin's pangenesis theory was complex as he tried to explain the process of sexual reproduction, passing of traits and complex developmentalDevelopmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
phenomena, such as cellular regeneration
Regeneration (biology)
In biology, regeneration is the process of renewal, restoration, and growth that makes genomes, cells, organs, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. Every species is capable of regeneration, from bacteria to humans. At its most...
. His pangenesis theory was criticised for its Lamarckian premise that parents could pass on traits acquired
Inheritance of acquired characters
The inheritance of acquired characteristics is a hypothesis that physiological changes acquired over the life of an organism may be transmitted to offspring...
in their lifetime. Lamarckism fell from favour after August Weismann's
August Weismann
Friedrich Leopold August Weismann was a German evolutionary biologist. Ernst Mayr ranked him the second most notable evolutionary theorist of the 19th century, after Charles Darwin...
research in the 1880s indicated that changes from use (such as lifting weights to increase muscle mass) and disuse (such as being lazy and becoming scrawny) were not heritable. Some Lamarckian principles, however, have not been entirely discounted and some of Darwin's pangenesis principles (in this regard) do relate to heritable aspects of phenotypic plasticity
Phenotypic plasticity
Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...
, while the status of gemmules has been firmly rejected. Darwin himself had noted that "the existence of free gemmules is a gratuitous assumption"; by some accounts in modern interpretation, gemmules may be considered a prescient mix of DNA, RNA, proteins, prions, and other mobile elements that are heritable in a non-Mendelian manner at the molecular level.
Later elaboration
In his later work, The Descent of Man, Darwin elaborated further on the model. In a section on the "Laws of inheritance," Darwin specified that two elements in particular were most important: the transmission and the development of inherited characteristics. Darwin's insights were that characteristics could be transmitted which were not at the time of transmission actually being manifest in the parent organism, and that certain traits would manifest themselves at the same point of development (say, old age) in both the parent and child organisms. In order to make sense of his theory of sexual selectionSexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
, he also stipulated that certain traits could be passed through organisms but would only develop depending on the sex of the organism in question.
Galton's experiments on rabbits
Darwin's half-cousin Francis GaltonFrancis Galton
Sir Francis Galton /ˈfrɑːnsɪs ˈgɔːltn̩/ FRS , cousin of Douglas Strutt Galton, half-cousin of Charles Darwin, was an English Victorian polymath: anthropologist, eugenicist, tropical explorer, geographer, inventor, meteorologist, proto-geneticist, psychometrician, and statistician...
conducted wide-ranging inquiries into heredity which led him to refute Charles Darwin's hypothetical theory of pangenesis. In consultation with Darwin, he set out to see if gemmules were transported in the blood. In a long series of experiments in 1869 to 1871, he transfused the blood between dissimilar breeds of rabbits, and examined the features of their offspring http://www.abc.net.au/rn/science/ss/stories/s216074.htm. He found no evidence of characters transmitted in the transfused blood . Darwin challenged the validity of Galton's experiment, giving his reasons in an article published in 'Nature'http://darwin-online.org.uk/content/frameset?itemID=F1751&viewtype=side&pageseq=1 where he wrote: "Now, in the chapter on Pangenesis in my Variation of Animals and Plants under Domestication, I have not said one word about the blood, or about any fluid proper to any circulating system. It is, indeed, obvious that the presence of gemmules in the blood can form no necessary part of my hypothesis; for I refer in illustration of it to the lowest animals, such as the Protozoa, which do not possess blood or any vessels; and I refer to plants in which the fluid, when present in the vessels, cannot be considered as true blood." He goes on to admit: "Nevertheless, when I first heard of Mr. Galton's experiments, I did not sufficiently reflect on the subject, and saw not the difficulty of believing in the presence of gemmules in the blood."
See also
- LamarckismLamarckismLamarckism is the idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring . It is named after the French biologist Jean-Baptiste Lamarck , who incorporated the action of soft inheritance into his evolutionary theories...
- Maupertuis as Pangenesis precursor
External links
- On-line Facsimile Edition of The Variation of Animals and Plants Under Domestication from Electronic Scholarly Publishing
- Variation under Domestication, From: Freeman, R. B. 1977. The Works of Charles Darwin: An Annotated Bibliographical Handlist. 2nd edn. Dawson: Folkstone, at DarwinOnline, with links to online versions of the 1st. edition, first and second issues, and the 2nd. edition.